1. Field of the Invention
The present invention relates to an optical disc having spare areas and a method therefor, and more particularly to a method for variable setting the rate of spare areas of an optical disc and an optical disc provided with the variable spare area rates.
2. Description of the Background Art
The recent development of the information industry increases the need for techniques capable of recording information of high density and large quantity. Especially, by entering the multimedia era, a remarkably rapid technical development has been achieved in recording optical media such as a compact disc (CD) and a digital versatile disc (DVD).
Along with such development and along with a demand for a recording medium of large capacity, optical recording media have become more popular than magnetic media. However, in employing the optical recording system, reliability of the recording substance of the optical disc, which is the recording medium, is inferior to the reliability of the magnetic disc. Techniques for compensating and/or correcting the inferior reliability have therefore been utilized using an error correction code, spare areas and so on.
Spare areas are set by portions in the recording area (i.e., a main area for storing a digital data) of the optical disc, which are not used during the normal recording condition. The spare areas are furnished for the purpose of providing a corresponding spare area that is equivalent to an area of the optical disc that is damaged and thus inoperative to permit the optical disc to normally function as the recording medium on the whole.
That is, the spare area is employed to prepare against damage to the recording area. Spare areas may be arranged at specific places of the optical disc or distributably arranged throughout respective portions within the disc. However, since the spare areas arranged to specific places of the optical disc induce unnecessary movement of the head during reading out and recording data, it is preferable that the spare areas are divided and distributably arranged throughout respective portions within the disc. Also, the recording areas of a recordable optical disc are set by employing a Zoned Constant Linear Velocity (ZCLV) system.
A general format of the above-stated optical disc is illustrated in FIG. 1. Referring to the optical disc 10 shown in FIG. 1, a reference numeral 1 denotes a radius of the disc; 2 is an inner radius of the disc; 3 is a recording area of the disc in which data is stored; 4 are zones divided into a plurality of partitioned areas in the diameter direction; and 5 are sectors divided in the circumferential direction within zones 4. Not shown in FIG. 1 are a plurality of tracks forming a concentric circle within zone 4.
The tracks, sectors 5 and zones 4 are respectively provided with independent addresses for easily reading out the recorded information, which facilitates the access to desired information by managing the file name of the recorded information and address with respect to the recorded position in accordance with a File Allocation Table (FAT).
In case of initializing the optical disc, the recording area is partitioned into 24 successive zones, and respective spare areas are allotted to zones 4. Because the foregoing spare areas are arranged within respective zones, the information to be recorded onto a portion that probably involves the faulty recording within the zone is recorded on the spare area within the corresponding zone to prevent the defect. The size of the spare area is adjustable. Thus, when the size is increased, the reliability of the disc is increased while the recording capacity is reduced relatively.
Therefore, the spare areas are allocated by a prescribed rate in accordance with the size (number of blocks) of the recording area within respective zones, and the size occupies approximately 5.37% which is the prescribed rate of the capacity of zones 4. The sizes of the spare areas per zone are indicated in the following <Table 1>.
TABLE 1Size of Recording AreaSize of Spare AreaZone(No. of blocks)(No. of blocks)Rate (%) 019011025.37% 120101085.37% 221221145.37% 322341205.37% 423461265.37% 524581325.37% 625701385.37% 726821445.37% 827921505.37% 929041565.37%1030161625.37%1131281685.37%1232401745.37%1333521805.37%1434641865.37%1535761925.37%1636861985.37%1737982045.37%1839102105.37%1940222165.37%2041342225.37%2142462285.37%2243582345.37%2344752405.37%Total7642441045.37%
<Table 1> is obtained by recording the spare areas produced from the DVD standard regulations.
The recording layer of the aforementioned optical disc is typically fabricated via a sputtering method which is widely used as one major technique of forming a this film. Here, it is required that the recording layer of the optical disc fabricated at this time has a characteristic of being consistent throughout the recording area. Accordingly, in order to uniformly maintain the quality of the optical disc, the certainty of such consistency becomes the important requisite.
FIG. 2 is a view showing a mean thickness distribution of the recording layer of the optical disc. As shown in FIG. 2, the center portion of the recording area has the relatively consistent thickness, but the portions adjacent to the inner circumferential portion or adjacent to the outer circumferential portion of the disc have the varied thickness. FIG. 2 also shows how the spare area rate remains constant along the radial direction of a conventional disc, as described above with respect to <Table 1>.
Furthermore during the injection molding for fabricating a substrate of the optical disc, which is formed of a plastic, the inner diameter portion and outer diameter portion of the disc are optically inconsistent due to the differences in resin temperature, cooling time, etc. The deviations of the recording characteristics incited due to the inconsistent substrate and varied thickness of the recording layer currently satisfy the stipulated standard of using the disc, which, however, are required to be improved in the aspect of reliability.
Therefore, many attempts have previously been made to achieve the desired consistency. Nevertheless, the thickness variation of the recording layer shows a deviation of ±2% currently. Additionally, it is a general point of view that the inconsistency is difficult to be completely eliminated.
As described above, the optical disc allots the spare areas of the prescribed rate (approximately 5.7%) with respect to overall zone capacity in setting the recording area. As described with reference to FIG. 2, the optical disc has inconsistent thickness throughout resulting from the varied thickness in the lengthwise direction of the radius. Consequently, since the defect occurring rates at specific points of the optical disc differ from one another, a specific zone cannot be used further if the defect within the corresponding zone is increased to employ all replaceable spare areas. For this reason, the overall disc may not be used without experiencing reduced reliability due to the increase of the defective portions.